Browsing by Author "Ross, Natasha"
Now showing 1 - 15 of 15
Results Per Page
Sort Options
Item Carbon supported aluminium trifluoride nanoparticles functionalized lithium manganese oxide for the development of advanced lithium ion battery system(University of the Western Cape, 2017) Willenberg, Shane; Ross, NatashaA novel lithium ion (Li-ion) battery cathode material has been investigated for potential mobile technology energy storage applications. I have successfully synthesized Lithium Manganese oxide (LMO), reduced Graphene Oxide (rGO) and Aluminium trifluoride (AlF3). The cathode coated nanocomposite was compiled of the aforementioned materials to give [AlF3LiMn2O4-rGO]. A single-phase spinel was observed from X-ray diffraction (XRD) studies with a high intensity (111) plane which indicates good electrochemical activity. No alterations to the crystal structure were observed after forming the composite nano-cathode material. Fourier transfer infrared (FTIR) spectroscopy showed the vibrational spectrum of LiMn2O4 with a with asymmetric MnO6 stretching confirming that the spinel was formed.Item A comparative energy storage efficiency study of multiple cation doped LiMxMn2-xO4/MWCNT cathodes for advanced Li-ion batteries(University of the Western Cape, 2022) Willenberg, Shane Clayton; Ross, NatashaThe current lithium-ion battery which is used in most technological applications is the LiCoO2 (LCO) battery. This battery offers a high theoretical capacity of 274 mAh.g-1. Scientists have however deemed this battery material as hazardous due to the toxicity of Cobalt and its explosive nature at high temperatures. LiMn2O4 (LMO) is considered to be substantially less toxic, cheaper than the LCO, and is also readily available in South Africa.Item Conductive composite biosensor system for electrochemical indinavir drug detection(HINDAWI LTD, 2015) Ross, Natasha; Hendricks-Leukes, Nicolette; Ajayi, Rachel FanelwaIndinavir is a protease inhibitor antiretroviral (ARV) drug, which forms part of the highly active antiretroviral therapy during the treatment of HIV/AIDS. Indinavir undergoes first-pass metabolism through the cytochrome P450 (CYP) enzymes in the human liver, of which CYP3A4 is the most influential isoenzyme. Multidrug combination therapy and, as such, therapeutic drug monitoring (TDM) during HIV/AIDS treatment are therefore critical, to prevent adverse interactions. The conventional sensitive and specific assays available for quantifying ARV drugs, however, suffer from distinct disadvantages. In this regard, biosensors can be used to provide real time information on the metabolic profile of the drug. In this study, a biosensor with cobalt(III) sepulchrate trichloride {Co(Sep) 3+} as diffusional mediator was constructed. The biosensor platform consisted of CYP3A4 immobilized onto a gold nanoparticle (GNP) overoxidized polypyrrole (OvOxPpy) carrier matrix. The biosensor exhibited reversible electrochemistry, with formal potential determined as ā624 Ā± 5 mV, from voltammetric analysis, with overall electron transfer being diffusion controlled. The biosensor showed typical electrocatalytic response to dioxygen (O2), exemplified by the distinct increase in the cathodic peak current (š¼š,š). A concentration-dependent increase in š¼š,š was observed in response to consecutive additions of Indinavir.Item Construction of an enzyme-free electrochemical sensor based on Ag-Fe2O3/POM/RGO novel nanocomposite for hydrogen peroxide detection(University of the Western Cape, 2018) Nqakala, Noniko Civilized; Ross, Natasha; Bilibana, Mawethu PascoeThe motivation to determine H2O2 lies in the fact that this chemical species plays a crucial role in diverse fields of practise such as cosmetic, food, diagnostic, pharmaceutical, clinical and environmental protection industries. Several methods such as chromatography, colorimetry, titrimetry and spectrophotometry have been developed for its detection. However, these methods are known to manifest underlying disadvantages such as high cost, time consuming, instability and complicated immobilization procedures. In this present study an enzyme-less electrochemical sensor based on Ag-Fe2O3/POM/RGO nanocomposite (POM stands for polyoxometalate and RGO stands for reduced graphene oxide) was successfully synthesised via a hydrothermal method and a photochemical reduction method for the detection of hydrogen peroxide (H2O2).Item Electrochemical determination of hydrogen peroxide by a nonenzymatic catalytically enhanced silver-iron (iii) oxide/polyoxometalate/reduced graphene oxide modified glassy carbon electrode(Taylor & Francis, 2020) Ross, Natasha; Civilized Nqakala, NonikoThe synergism of phosphomolybdic acid hydrate (POM) decorated with silver-iron (III) oxide (Ag-Fe2O3) nanoparticles and anchored on reduced graphene oxide (RGO) have been demonstrated to be effective as a nonenzymatic H2O2 sensor platform. The assembly of the sensor components and their interactions were probed morphologically, spectroscopically and electrochemically. The Ag-Fe2O3/POM/RGO nanocomposite sensor provided an enhanced electroactive surface area, electrical conductivity and sensitivity for hydrogen peroxide compared to an unmodified glassy carbon electrode (GCE) at ā0.55 V versus a saturated calomel electrode. The developed sensor amperometric response was linear across the concentration range from 0.3 mM to 3.3 mM (R2 = 0.992) with a detection limit and sensitivity of 0.2 Ī¼M and 271 Ī¼AĀ·mMā1Ā·cmā2 respectively. Concomitantly, a short response time of T90 < 5 sec at a signal-to-noise ratio of 4 was achieved. The sensor was shown to determine hydrogen in the presence of interfering species, and exhibited high selectivity with relative standard deviation values less than 4.2%. The results indicate that the use of RGO to anchor and photochemically reduce POM also improved the reduction properties due to the irregular size distribution and catalytic activity of Ag-Fe2O3 stimulated by its adhesion to the distinctive POM/RGO matrix.Item Electrochemically enhanced ferric lithium manganese phosphate / multi-walled carbon nanotube, as a possible composite cathode material for lithium ion battery(University of the Western Cape, 2019) Sifuba, Sabelo; Ross, Natasha; Iwuoha, Emmanuel; Feleni, UsisiphoLithium iron manganese phosphate (LiFe0.5Mn0.5PO4), is a promising, low cost and high energy density (700 Wh/kg) cathode material with high theoretical capacity and high operating voltage of 4.1 V vs. Li/Li+, which falls within the electrochemical stability window of conventional electrolyte solutions. However, a key problem prohibiting it from large scale commercialization is its severe capacity fading during cycling. The improvement of its electrochemical cycling stability is greatly attributed to the suppression of Jahn-Teller distortion at the surface of the LiFe0.5Mn0.5PO4 particles. Nanostructured materials offered advantages of a large surface to volume ratio, efficient electron conducting pathways and facile strain relaxation. The LiFe0.5Mn0.5PO4 nanoparticles were synthesized via a simple-facile microwave method followed by coating with multi-walled carbon nanotubes (MWCNTs) nanoparticles to enhance electrical and thermal conductivity. The pristine LiFe0.5Mn0.5PO4 and LiFe0.5Mn0.5PO4-MWCNTs composite were examined using a combination of spectroscopic and microscopic techniques along with electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Microscopic results revealed that the LiFe0.5Mn0.5PO4-MWCNTs composite contains well crystallized particles and regular morphological structures with narrow size distributions. The composite cathode exhibits better reversibility and kinetics than the pristine LiFe0.5Mn0.5PO4 due to the presence of the conductive additives in the LiFe0.5Mn0.5PO4-MWCNTs composite. For the composite cathode, D = 2.0 x 10-9 cm2/s while for pristine LiFe0.5Mn0.5PO4 D = 4.81 x 10-10 cm2/s. The charge capacity and the discharge capacity for LiFe0.5Mn0.5PO4-MWCNTs composite were 259.9 mAh/g and 177.6 mAh/g, respectively, at 0.01 V/s. The corresponding values for pristine LiFe0.5Mn0.5PO4 were 115 mAh/g and 44.75 mAh/g, respectively. This was corroborated by EIS measurements. LiFe0.5Mn0.5PO4-MWCNTs composite showed to have better conductivity which corresponded to faster electron transfer and therefore better electrochemical performance than pristine LiFe0.5Mn0.5PO4. The composite cathode material (LiFe0.5Mn0.5PO4-MWCNTs) with improved electronic conductivity holds great promise for enhancing electrochemical performances and the suppression of the reductive decomposition of the electrolyte solution on the LiFe0.5Mn0.5PO4 surface. This study proposes an easy to scale-up and cost-effective technique for producing novel high-performance nanostructured LiFe0.5Mn0.5PO4 nano-powder cathode material.Item Nano silver-iron-reduced graphene oxide modified titanium dioxide photocatalyst for the remediation of organic dye in water systems(University of the Western Cape, 2018) Sass, Danielle Thandi; Ross, NatashaDrinking water with high concentrations of inorganic and organic contaminants can cause adverse health defects. Specifically methyl orange dye is an organic water contaminant that has been known (along with others like methyl blue etc.) to have an increase in our water systems over the past few years due to increasing demand in industrial processes. It is therefore of utmost importance to remediate organic contaminants and ultimately enable prevention. The contaminants can be removed by photocatalysis. Anatase TiO2 is known for its photocatalytic degradation of environmental pollutants and photoelectro-chemical conversion of solar energy. However its application is limited since it is a wide band gap semiconductor, (Eg = 3.2 eV). The following study deals with the enhancement of the photocatalytic properties of TiO2 for remediation of organic water contaminants.Item Nano silver-Iron-reduced graphene oxide modified titanium dioxide photocatalyst for the remediation of Organic dye in water systems(University of the Western Cape, 2018) Sass, Danielle; Ross, Natasha; Iwuoha, EmmanuelDrinking water with high concentrations of inorganic and organic contaminants can cause adverse health defects. Specifically methyl orange dye is an organic water contaminant that has been known (along with others like methyl blue etc.) to have an increase in our water systems over the past few years due to increasing demand in industrial processes. It is therefore of utmost importance to remediate organic contaminants and ultimately enable prevention. The contaminants can be removed by photocatalysis. Anatase TiO2 is known for its photocatalytic degradation of environmental pollutants and photoelectro-chemical conversion of solar energy. However its application is limited since it is a wide band gap semiconductor, (Eg = 3.2 eV). The following study deals with the enhancement of the photocatalytic properties of TiO2 for remediation of organic water contaminants. The study was carried out to produce the two nanocomposites AgFe-TiO2 and AgFe-TiO2-rGO photocatalyst which purpose is to be cheap and easy to apply, with improved (fast and effective) photocatalytic degradation of methyl orange. The main objective was to decrease the band gap and to introduce intra-band gap states to absorb visible light. Modification of the TiO2 with small bandgap semiconductor, graphene and Ag- Fe nanoalloy reduced the bandgap energy for visible light absorption and photocatalytic degradation of methyl orange dye. The two composites were synthesised using sonication and chemical synthesis methods. A photocatalytic study (degradation of methyl orange dye) was carried out using a system incorporating an UV lamp source to determine the degradation of methyl orange catalysed by the synthesised photocatalysts AgFe-TiO2-rGO and AgFe-TiO2 along with UV-vis Spectroscopy. Morphological studies were carried out using HRSEM and HRTEM which determined the spherical agglomerated nature of AgFe-TiO2 and the sheet-like nature of AgFe-TiO2-rGO containing spherical agglomerants but that also contained pockets formed by the sheets of the rGO. XRD served as confirmation of the phase of TiO2 in both composites to be anatase. Analysis confirmed the formation and elemental determination of both composites. It was observed that the Band gap of TiO2 degussa decreased from 2.94 eV to 2.77 eV in the composite AgFe-TiO2. The photocatalytic reactivity of AgFe- TiO2 was an improvement from TiO2 and AgFe-TiO2-rGO based on the photocatalytic study. Therefore concluding that AgFe-TiO2 was the best catalyst to convert the dye (Orange II) into free radicals and ultimately remove the contaminant from the water compared to AgFe-TiO2-rGO.Item The nano-optimization of p- and e-type semiconductor films for efficient perovskite photovoltaics(University of the Western Cape, 2022) Orange, Tamsen; Ross, NatashaPerovskite solar cells (PSCs) have gained a lot of attraction due to the multiple existing, inexpensive production methods, the flexibility of materials and structures that can be utilized, and the outstanding optoelectric properties, which include the high carrier diffusion length and strong absorption. Despite the multiple favourable characteristics, there are however unfavourable characteristics that are preventing the commercialization of these solar cells, namely, the scaling up of the spin-coating process, the stability of the cells, the toxicity because of the lead compounds used in the cells, and hysteresis in current-voltage (I-V) curves. Structural stability refers to the capability of the crystalline stage to resist degradation over a wide range of conditions, namely, moisture, pressure, and heat.Item Nanostructured materials for sustainable next generation organic solar cells(University of the Western Cape, 2022) Mabindisa, Rorisang; Ross, NatashaMany researchers are conducting their studies that are centred on using solar energy to generate electricity due to the developing interest in solar energy. One of the most promising options to reduce the cost of manufacturing photovoltaic cells and increase power conversion efficiency in the framework of solar energy is hybrid photovoltaics, which combines organic molecules and nanomaterials. Photovoltaic cells become significant in this regard. Most of the commercially accessible photovoltaic cells currently are made of inorganic materials, which are expensive to produce and include harmful compounds. Because of these factors, organic photovoltaic cells have an advantage over their inorganic counterparts. In this research project, we concentrated on synthesising new donor nanostructured materials for use in organic photovoltaic cells. A range of characterisation techniques were used to confirm and analyse the compounds that are commercially available with the newly as-synthesised compound.Item P- and e- type Semiconductor layers optimization for efficient perovskite photovoltaics(University of Western Cape, 2019) Tambwe, Kevin; Ross, Natasha; Baker, PriscillaPerovskite solar cells have attracted a tremendous amount of research interest in the scientific community recently, owing to their remarkable performance reaching up to 22% power conversion efficiency (PCE) in merely 6 to 7 years of development. Numerous advantages such as reduced price of raw materials, ease of fabrication and so on, have contributed to their increased popularity.Item p- and e- type Semiconductor layers optimization for efficient perovskite photovoltaics(University of the Western Cape, 2019) Tambwe, Kevin; Ross, NatashaPerovskite solar cells have attracted a tremendous amount of research interest in the scientific community recently, owing to their remarkable performance reaching up to 22% power conversion efficiency (PCE) in merely 6 to 7 years of development. Numerous advantages such as reduced price of raw materials, ease of fabrication and so on, have contributed to their increased popularity. However, there are several factors that limits their performance, among which is recombination process of charge carriers occurring at the TiO2/Perovskite interface. Therefore, it is crucial to prevent charge carriers recombination at the photo anode/electrode interface, in order to improve the overall efficiency of the Perovskite solar cell (PSC) devices.Item Palladium-gold nanoalloy surface modified limn2o4 cathode for enhanced li-ion battery(Hindawi, 2015) Ross, Natasha; Nzaba, Myra; Ntuthuko, WonderboyAu with Pd nanoparticles were synthesized and coated onto the spinel LiMn2O4 via a coprecipitation calcination method with the objective to improve the microstructure, conductivity, and electrochemical activities of pristine LiMn2O4. The novel Li[PdAu]š„Mn2āš„O4 composite cathode had high phase purity, well crystallized particles, and more regular morphological structures with narrow size distributions. At enlarged cycling potential ranges the Li[PdAu]š„Mn2āš„O4 sample delivered 90 mAh gā1 discharge capacity compared to LiMn2O4 (45 mAh gā1). It was concluded that even a small amount of the Pd and Au enhanced both the lithium diffusivity and electrochemical conductivity of the host sample due to the beneficial properties of their synergy. Lithium-ion batteries are becoming incredibly popular in modern electronic devices. Compared with traditional battery technology, lithium-ion batteries charge faster, with an operating voltage of ā¼3.7 V, last longer, and have a higher power density in a lighter package [1].Item Scalable synthesis of innovative silicon/carbon nanocomposite for next generation lithium-ion battery anodes(University of the Western Cape, 2022) Larkin, Roy-John; Ross, NatashaSilicon is the most promising lithium-ion battery (LIB) anode due to its ultra-high capacity (4200 mAh/g), which is 10 times greater than commercially available graphite anodes (372 mAh/g). Utilizing this large capacity allows for the development of high-performance LIBs for next generation innovative applications. However, during lithiation/delithiation, silicon anodes experience a volume change of over 300% which leads to mechanical and electrochemical degradation that limits cycle efficiency and life span. To remedy this limitation, porous silicon nanoparticles were composited with CNTs - as it produces mechanically stable architectures capable of buffering large volume changes.Item Spectroscopic and electrochemical exploration of carbon-infused intercalation-type spinel composite for aqueous systems(Frontiers Media, 2022) Willenberg, Shane; Carleschi, Emanuela; Ross, NatashaLithium-manganese-based compounds are promising intercalation host materials for aqueous battery systems due to their synergy with high ionic conductive aqueous electrolytes, safety, eco-friendliness, and low cost. Yet, due to poor electrical conductivity and trapping of diffused electrolyte cations within its crystal formation, achieving optimum cycle stability and rate capability remains a challenge. This unfortunately limits their use in modern day high-powered devices, which require quality output with high reliability. Here, the authors propose a facile method to produce LiMn2O4 and LiFe0.5Mn0.5PO4 and compare their structural stability and corresponding electrochemical performance by controlling the interfacial layer through multi-walled carbon nanotubesā (MWCNTs) infusion.